General

The Occluder helps with optimizing the scene in addition to View Frustum Culling, Small Feature Culling? and Level Of Detail OSG LOD nodes. If an object is completely occluded by the Occluder-object, it wil not be rendered. If only a small part of the object is outside the Occluder-object it WILL be rendered.

Possible uses

In a city scene it is imaginable that a lot of the building could act as an Occluder, preventing someone form viewing other building behind them. Since they are still within the view frustum, they will be rendered. If an Occluder was present, this would not happen, thus rendering would be faster.

To create an Occluder Helper in 3d Studio Max

Create geometry;

Create a closed shape (e.g. a rectangle) in front of this geometry;

Add an Occluder Helper to the scene;

Add the shape to the Occluder Helper.

This images shows the way an Occluder is setup: between viewer (red dot) and objects

Demonstration

The model used was a small log cabin downloaded from the [internet]. A red dot was placed in the scene for reference. As you can see in the first picture, when looked at from the side, both objects are visible. Standing at the position of the red dot, the house gets occluded and is not rendered. You can download the model used for this demonstration. The MAX, OSG and image-files are included in the archive.